1. Field of the Invention
The present invention relates to a method of drying a wet green body such as an undried green honeycomb structure using a microwave.
2. Description of the Prior Art
A honeycomb structure is widely used for a catalyst carrier and various filters, and recently has also attracted attention as a diesel particulate filter (DPF) for capturing particulates discharged from a diesel engine.
Honeycomb structures are made of a ceramics as major components. These honeycomb structures are usually manufactured by preparing clay by kneading a mixture of ceramic raw materials with water and various additives, extruding thus prepared clay into a formed product to obtain undried green honeycomb structures (hereinafter sometimes referred to as formed honeycomb structures), drying thus formed green honeycomb structures, and firing the resultant dried honeycomb structures.
A well known method of drying the formed honeycomb is a dielectric drying method in which high frequency energy generated by passing a current between electrodes installed in the upper portion and lower portion of the formed honeycomb product is used for drying. A hot air drying method in which a hot wind produced by a gas burner or the like is used is also well known. In recent years, a drying method using a microwave is used in place of or in combination with these drying techniques because of its advantages such as high drying speed and the reduced risk of deforming the objects to be dried.
In general, the microwave drying method is carried out by horizontally laying two or more objects to be dried in a same given space, such as a drying chamber of an oven, and irradiating the objects with a microwave generated by a microwave generating apparatus (See for example JP-A-2002-283329).
To increase productivity in drying formed honeycomb structures using the microwave drying method, it is desirable to minimize the distance between the objects to be dried that are laid within the same space such as turn tables or belt conveyers installed within the drying oven, thereby the number of the objects to be dried in one operation can be maximized. However, too narrow a distance between the objects to be dried causes a problem. This is because the uniform drying of all the objects laid within the same given space becomes difficult since the drying conditions would often vary, one by one within the objects laid in the same given space, depending upon the mutual distance between them.